Customers of security lock systems have recognized the importance of having high security mechanisms on vulnerable doors. The protection offered by these cylinders more than justifies their cost. However the expense to equip all the doors in a facility with modern high security cylinders often offsets the potential benefit of having high security cylinders on nonessential doors. Many customers choose to install and maintain two different master key systems, one for the high security doors and one for the common, less critical doors, thus having more keys to manage and carry for access.
This has lead to the development of so-called hierarchical lock systems. A hierarchical lock system includes one or more high security cylinders, typically installed on critical, high-risk doors, and associated lower security cylinders installed on less critical doors. The lower security cylinders are “associated” with the high security cylinders in the sense that a high-security master key, capable of operating the high security cylinder, is also capable of operating each of the associated lower security cylinders. Lower security keys for operating the associated lower security cylinders are not, however, capable of operating the high security cylinders with which the cylinders are associated. Each lower security cylinder may also have one or more associated cylinders of still lower security. And any key capable of operating cylinders at one security level is also capable of operating associated cylinders at lower levels, but the keys constructed to operate only lower security cylinders cannot operate higher security cylinders with which the lower security cylinders are associated.
In the context of this description, a standard security cylinder is a cylinder having fewer security features than a high security cylinder. The standard security cylinder is not necessarily the cylinder with the fewest security features within any particular hierarchical scheme.
Several lock manufacturers currently make cylinders that can be arranged into systems with different levels of physical security. As the industry produces new and higher security products it is necessary to develop standard security lock cylinders (i.e., non-high security cylinders) that will interface into systems with the newer high security cylinders and be operated by the high security keys. Notwithstanding improvements in the well worked lock art, there remains a need for lock cylinders which offer different levels of protection against criminal attack or other unauthorized entry and which can be arranged into one hierarchical keying schedule. Such lock mechanisms should also resist contemporary lock picking techniques, and it is desirable that the dimensions of the lock not exceed conventional cylinder size. It is equally important that the components and the lock assembly can be economically mass produced.